Conventionally, those applied as this type of sealing apparatus are described in patent document 1 (Japanese Patent Application Laid-open No. 11-125338) and patent document 2 (Japanese Patent Application Laid-open No. 2002-98163).
Particularly, as a specific example of one such as described in patent document 2, there is one shown in FIG. 5 (See FIG. 2 of patent document 2). FIG. 5 is a half sectional view of a sealing apparatus 101 according to a conventional art.
In FIG. 5, sealing apparatus 101 is arranged between a cap into which an end portion of a cross shaft is inserted and fitted and the end portion of the cross shaft.
Sealing apparatus 101 has an attachment portion 102 attached to the cap. A metal ring 103 is integrally formed on the surface of attachment portion 102, and this metal ring 103 is press-fitted to the cap.
Then, a sealing lip 104 that extends from attachment portion 102 is slidably in sealing contact with the outer periphery of the cross shaft.
Also, on an open-air side A of sealing lip 104, double dust lips 105, 106 are slidably in contact with the outer periphery of the cross shaft.
The sealing lip 104 and dust lips 105, 106 extend from attachment portion 102 to the cross shaft on the inner side while being tilted to the open-air side A.
Here, the tip end of sealing lip 104 has an inner side contact angle a which is an angle smaller than an open-air side contact angle β (α<β), and is provided as a so-called outward-oriented lip.
The purpose of setting such a relationship of the contact angles of the outward-oriented lip is to prevent occurrence of lip inversion caused by generation of inner pressure and to allow the grease supplied to bearings on an inner side I to escape to the open-air side A.